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Characterization and Suitability Evaluation of Soils
over Sandstone for Cashew (Anacardium occidentale
L) Production in a Nigerian Southern Guinea
Savanna
Ofem, K. I1., Abua, S.O1., Umeugokwe, C.P2., Ezeaku, V. I2. and Akpan-Idiok, A. U1
1Department of Soil Science, University of Calabar, Nigeria 2Department of Soil Science, University of Nigeria, Nsukka
DOI: 10.29322/IJSRP.10.07.2020.p10342
http://dx.doi.org/10.29322/IJSRP.10.07.2020.p10342
Abstract- The study examined the properties as well as the Taxonomic classification of soils developed on sandstone in the
Southern Guinea Savanna of Nigeria. The soils were also evaluated for their suitability for cashew production. The contour
map of Bekwarra was obtained in the ArcGIS 10.2.1.3 environment and two profile graphs plotted to represent two
toposequences. Six profile pits were then sited. The soils were deep (>100 cm) to weathered rock with argillic B horizons.
The surface soils were dark reddish brown (5YR 3/4) to very dark gray (2.5YR 3/1) and gray (7.5YR 5/1). Soil bulk density
was < 1.60 Mg/m3. Amount of clay fluctuated with soil depth while sand fraction dominated the soils. Irrespective of
landscape position, the soils were severe to moderately acid in reaction, and low to moderate in organic carbon. The soils
were moderate in exchangeable Ca2+ and Mg2+ and low in K+ and Na+. The soils were moderately suitable (S2) and currently
not suitable (N1), potentially for cashew production. Pedon 1 was classified as Typic Haplustalf (Haplic Luvisols), pedons
2, 3 and 4 as Typic Paleustalfs (Haplic Luvisols) while pedon 4 was Rhodic Luvisols in the WRBSR system. Soils at the
valley bottom were classified as Aquic Udorthents (Hypereutric Gleysols). Site specific conservation farming, combined
application of organic and inorganic fertilizers as well as the application of calcite and dolomite at appropriate dosages are
advocated. Furthermore, it is pertinent to change land use of the soils at the valley bottom (pedons 5 & 6).
Index Terms- Soil characterization; classification; toposequence; suitability; cashew
I. INTRODUCTION
and forms in the sub humid tropics are generally characterized by rolling topography and small valleys; soils formed
along such slopes often vary in basic properties and classification. Hence, the agricultural land use potentials of soils
along different landscape positions also differ. Sustainable agriculture rests on the in-depth study as well as inventorization
of soil resources, consequently, inadequate information on the soil resources of any region contributes to the problem of soil
degradation as well as food insecurity.
Different rates of weathering of parent materials, the nutrients they contain for plant use and dominant particle size
are some ways in which parent materials influence soil formation. Parent materials are important soil forming factor that
contribute to the differences in soil properties (Ibangha, 2006; Esu, 2010). However, Akamigbo and Asadu (1982) observed
that parent materials have very significant influence on the overlying soil when the soil is formed in situ. Sandstone on
which the soils under study is formed is medium grained and composed of quartz and clastic in origin, and occurs in the
major ecological zones of Nigeria (Ogunwale and Ashaye, 1975). Soils developed on sandstone are shallow, sandy and
gravelly, and are generally erodible (Bulktrade, 1989). Such soils in the Niger Delta area and particularly Akwa Ibom State
are fragile, acidic and low in native fertility, and are described as marginal by farmers in the area (Udoh et al., 2015).
Adequate information on land resources has been identified as a pre-requisite for sustainable land management (Ofem
et al., 2016), consequently, Esu (2004) advocated detailed study of soil resources through soil characterization and land
evaluation. Land suitability evaluation is a simple avenue to combat the many problems linked to land use (Ofem et al.,
2016). It also helps individual land owners and regional development agencies to make valid national decisions among
available land use and site selection options (Esu, 2013; Widiatmaka et al., 2014), and makes it even more necessary to
know how suitable the land is for Cashew production.
Cashew has an architecture for reclaiming tracts of land to enhance its productivity (Adeigbe et al., 2015). Nearly 90
% of the lateral roots of cashew concentrate in the upper 15-45 cm of the soil while its tap root may extend up to a depth of
about 5 m (Schoenmaker, 1998). The crop requires deep, well drained and light to medium textured soils (Sys et al., 1993).
Its young tap root is sensitive to physical soil limitation (Ngatunga et al., 2001) and requires optimum pH of 4.5-6.5 (FAO,
1994). However, Sys et al. (1993) recommended an optimum pH of 5.5-7.0. Furthermore, organic carbon of over 0.8 %,
CEC of over 12.4 cmol/kg and loam textures with a minimum effective soil depth of 40 cm were recommended for
productivity above 80 % (Widiatmaka et al., 2014). The crop is draught resistant and requires hot conditions, as frost
L
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conditions may result in black nuts or rots (Sys et al. (1993). Consequently, cashew productivity decreases with higher
rainfall.
Economically, cashew nut accounts for 7-8 % of non-oil export earnings in Nigeria with an estimated USD 25-35
million per year (Nugawela & Oroch, 2005). Production increased from 30,000 in 1990 to 836,500 MT in 2012 (FAOSTAT,
2013). Majority of such export quality come from the eastern and western Nigeria (Adeigbe et al., 2015). Nigeria was ranked
second in the world, next to only Vietnam and first in Africa in 2010, 2011 and 2012 with production estimated at 650000,
813023 and 835500 MT, respectively (Ogunsinan & Lucas, 2008 & FAOSTAT, 2013). Since 2014, cashew has become the
second main cash crop in west Africa behind cocoa and ahead of cotton, rubber, palm oil or banana (Nitidae, 2019). In 2018,
250,000 MT was produced in Nigeria from an area of 755,000 ha (Nitidae, 2019).
The agricultural potentials of the soils have not been fully harnessed due to scanty recent research on the soils; hence
the adoption of wrong land management methods and land use types by the farmers who are either not exposed to relevant
information regarding the soils they intend to cultivate or such information are too cumbersome for their understanding.
This has resulted in underutilization and degradation of the soils as they are often not used for what their characteristics
match for. It is therefore apt to study the soils in order to bridge the gap in soil resource information and also expand on
their agricultural use options through suitability evaluation for cashew production. Although the soils have been adjudged
to be low in fertility status (Udoh et al., 2015), oil palm, cashew, rice and maize as well as cassava, sorghum and yam have
been found to have comparative advantage over other crops. This study is therefore saddled with the responsibility of
characterizing and taxonomically classifying the soils based on the criteria of USDA and correlating same with the World
Reference Base for Soil Resources System. Suitability evaluation of the land will also be carried out to ascertain its fitness
and possible consideration for intensive and commercial production of cashew.
II. MATERIALS AND METHOD
Environment of study area
The study was sited in Bekwarra Local Government Area (LGA) of Northern Cross River State. It lies in the southern
guinea savanna of Nigeria with patches of rainforest and located between longitudes 4o21' and 6o45'E, and latitudes 7o15'
and 9o28'N. It is bounded to the North by Vandikyia in Benue State and to the East by Obudu cattle ranch. Soils in the area
are developed on sedimentary formation which constitutes fine grained sandstone, shales and siltstone with local occurrences
of limestone (Bulktrade, 1989). The study area varies between level to nearly level and gently undulating local relief with
pronounce hills. Rainfall varies between 1251.4 and 3347.8 mm/annum while range of 22.96-33.75 oC characterizes
temperature in the area (Sambo et al. 2016). Mean relative humidity was reported as 72.14 % while evaporation rate had
mean value of 2.24 mm/day and range of 1.8-2.8 mm/day. The area is dominated by grass species like; Andropogon spp.,
Imperata cylindrical, Combretum spp., Panicum maximum and tree species like Elaeis guineensis, Bukrea Africana,
Gmelina aborea, and Anacardium occidentale.
Field studies
The contour map of Bekwarra was obtained in the ArcGIS 10.2.1.3 environment. Considering the distribution of
elevations on the contours, topo-positions were identified and two profile graphs plotted to represent two toposequences.
Each toposequence was located in Anyikang and Ibiaragiri (Fig. 1). These are major agrarian communities in Bekwarra
LGA. These locations have major advantages for the production of cashew in the area. Upon field reconnaissance
verification, point locations representing soil profile pits were obtained with the aid of the GPS device. Soil profile pits were
then sited in the summit, middle slope and valley bottom positions of each toposequence to represent the soils. Furthermore,
pedons were dug and described according to the requirements of Soil Survey Staff (2012). Soil samples were obtained from
pedogenic horizons, labeled and transported to the laboratory for analysis. Samples meant for bulk density determination
were collected with the aid of cylindrical cores that were drilled vertically downwards. The core samples were oven dried
at 105 oC until constant weight was obtained.
Laboratory studies Soil samples were air dried under laboratory conditions, grinded and sieved through a 2 mm mesh. The fine earth fraction
(< 2 mm) was used for various laboratory analyses. Particle size analysis of was done by the Bouyoucos hydrometer method
using sodium hexametaphosphate as the dispersant (Gee and Bauder, 1986) while bulk density (Bd) was determined by
undisturbed core cylinder (Blake, 1965) and particle density (Pd) was determined by the use of a pycnometer (Bowles,
1992). Consequently,total porosity (Tp) was determined from the expression: TP = (1 - Bd/Pd) × 100. Soil pH was
determined in a soil to water ratio of 1:1 using a glass electrode pH meter while soil organic carbon was obtained by the
Walkley and Black wet oxidation method and total N was determined by the macro Kjeldahl digestion method (Udo et al.,
2009). Bray 1 solution was used as extractant in the colorimetric determination of available P while exchangeable bases
were extracted with 1 N neutral NH4OAc. Exchangeable Ca and Mg were thereafter obtained by the Versenate EDTA
titration method while K and Na were determined with the aid of a flame photometer (Udo et al., 2009). Cation exchange
capacity was determined in neutral NH4OAc as outlined by Udo et al. (2009) while base saturation was obtained by
expressing the sum of exchangeable bases as a percentage of the CEC by NH4OAc at 7.0.
Land suitability evaluation procedures
Land suitability for cashew production was according to the requirements of Sys et al. (1993) (Table 4). The pedons
were placed in suitability classes by comparing the data obtained in the study area (Table 3) to cashew requirement (Table
1). The most limiting factor was used to determine the overall suitability ratings in accordance with Liebig’s law of
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minimum.
For the parametric (square root
method) method, each limiting
characteristic was rated as shown in Table
1. The potential and current indices of
productivity (IP) for each pedon were
computed using the equation:
IP = A √B/100 * C/100 …. E/100; Where:
A = Overall lowest characteristic rating;
B, C … E = The lowest characteristic
rating for each land quality group.
Since there are often strong
correlations within a land quality group,
only one member with the least rating in
each of climate (c), wetness (w), physical
soil characteristics (s), soil fertility (f) and
available nutrients (a) were used to
calculate the index of productivity;
current and potential productivity. In
potential productivity, properties (organic
C, total N and available P) that are easily
altered by soil management procedures
were masked.
Fig. 1: contour and location map of Bekwarra with profile points
Table 1: Land requirement for Oil palm production indicating; Class, degree of limitation and rating scale
Land S1 S2 S3 N1 N2
Characteristics 0 1 2 3 4
Rating scale 100-95 95-85 85-60 60-40 40-25 25-0
Climate (c) MAR(mm/yr) 1800-1600 1600-1200 1200-800 800-500 - <500
1800-2000 2000-3000 3000-3800 >3800 - -
MAT (oC) >25 25-22 22-20 <20 - -
Wetness (w)
Flooding Fo - - - - F1+
(No flooding) - Severe; Every
year
Drainage Good,
moderate
Good; moderate Imperfect +
Fluctuating H2O
Imperfect +
Permanent high
Poor but
drainable
Poor; not
drainable
Physical soil characteristics (s)
Texture C, SiC, SiCL,
CL, SiL, SC
C,L,LfS,SCL,SL fS, LCS S, CS - SiC
Soil depth (cm) >150 150-100 100-50 50-25 - <25
Soil fertility characteristics (f)
*CEC (cmol/kg) >12.4 8.5-12.4 2.6-8.5 <2.6 - -
BS (%) >35 35-20 <20 - - -
pH (H2O) 6.0-5.5, 6.0-
7.0
5.5-5.2, 7.0-7.5 5.2-4.8, 7.5-8.0 4.8-4.5, 8.0-8.5 <4.5 >8.5
Org. C (%) >1.5 1.5-0.8 <0.8 - - -
Available nutrients (a)
*Total N (%) >0.07 0.05-0.07 0.03-0.05 <0.03 - -
*AvailableP(ppm) >40 11-40 1-11 <1.0 - -
*Exch.K(cmol/kg) >0.37 0.27-0.37 0.10-0.27 <0.10 - -
Source: Sys et al. (1993); *Widiatmaka et al. (2014)
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III. RESULTS AND DISCUSSION
Soil morphological properties
Dark reddish brown (5YR 3/4, 2.5YR 2.5/4), very dark greyish brown (10YR 3/2) to dark brown (10YR 3/3), and very
dark gray (2.5YR 3/1) overlaid dark red (2.5YR 3/6) to red (2.5YR 4/8), dark brown (7.5YR 3/3) and red (2.5YR 4/6), and
gray (7.5YR 5/1) colours in the crest, middle slope and valley bottom, respectively (Tables 2a,b,c). Reddish soil colour in
the crest and middle slope is indicative of the presence of oxides and oxyhydroxides of iron and aluminum, and further
suggests soil maturity or well-drained condition. Souza et al. (2019) attributed such colours to the presence of goethite and
hematite.
Table 2a: Morphological properties of the soils
Horizon Depth
(cm)
Soil Colour
(moist)
Mottling Texture Structure Consistence Boundary Other characteristics
Crestal soils
Pedon 1 (N06o40'500'', E 008o52'054'', 120m ASL)
Ap
Bt
Cr1
Cr2
0 – 33
33 – 72
72 – 133
133 – 200
2.5YR 2.5/4
2.5YR 4/8
2.5YR 4/8
2.5YR 4/8
-
-
-
-
gsl
scl
sl
sl
Wfgbk
mfmsbk
mmsbk
wmsbk
wss; mvfr
wns; mvfr
wns; mvfr
wns; mvfr
cs
cw
gs
-
Medium common pores;
many coarse roots; few iron
nodules; quartz mineral;
many ants and termites.
Common moderate clay and
iron cutans on pores;
common many fine medium
roots; iron nodules; many
quartz; few ants and termites.
Few thin cutans pores; few
common coarse roots; iron
nodules; many quartz.
Few fine pores; few medium
roots; few iron nodules and
many quartz.
Pedon 2 (N06o40'932'', E 008o53'663'', 145 m ASL)
Ap
Bt
Cr1
Cr2
0 – 28
28 – 105
105 – 147
147 – 200
5YR 3/4
2.5YR 4/8
2.5YR 3/6
2.5YR 3/6
-
-
-
-
scl
sc
sc
gsc
2m sbk
2m sbk
wm sbk
wm sbk
wss; mfr
wss; mf
wss; mvfr
ws; ,mvfr
cs
cw
gs
-
Very few fine thin clay
cutans pores; many common
pores; common medium
roots; ants and termites.
Few thin clay cutans pores;
common medium roots;
termites and ants; rock
outcrop.
Very few thin clay cutans on
pores; few very fine pores;
few very fine roots; ants,
termites.
Few moderate clays and iron
cutans on ped faces; iron
nodules; quartz; oxides of
iron.
On the other hand, dark and brown colours common in the surface soils are due to the presence of decomposed organic
matter. This result is similar to those of Bulktrade (1989) in the study area and Ahukaemere et al. (2013) on similar soils
elsewhere. Furthermore, gray colours obtained in the valley bottom soils indicates loss of oxides of Fe and Al, as well as
wetting. Similar colours were obtained by Ukut et al. (2014).
Irrespective of the landscape positions, textural class in the surface soils was mainly loam with variable sand content
giving rise to sandy loam and sandy clay loam. The subsurface soils seemed to have similar or finer textures across the
landscapes. This suggests greater vertical than lateral movement of fine particles. Such textures are typical of sandstone
soils and are responsible for the well-drained soil condition. Similar textures were obtained by Bulktrade (1989) while
Laffan et al. (1998) obtained sandy loam, loamy sand and clay textures in the sandstone soils of Northern Tasmania, New
Zealand.
Soil consistence in the crest was slightly sticky when wet, and friable to very friable in moist condition for the surface
soils while the underlying soils were more sticky (Tables 2a,b,c). However, consistence under moist condition ranged from
friable to very friable and firm in the middle slope and valley bottom (Tables 2b,c). Ahukaemere et al. (2013) had consistence
varying from friable to very firm in the surface soils and very friable to firm in the subsurface soils. Plant roots, ants and
termites beyond 122 cm indicate the absence of physical impediments, as well as the availability of water and nutrients at
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such depths. Ants, worms and termites encourage decomposition and soil mixing. Clay cutans were found in almost all the
subsurface horizons of the crest and middle slope soils (Tables 2a,b), and indicates soil maturity.
Table 2b: Morphological properties of soils at the middle slope
Horizon Depth (cm) Soil Colour
(moist)
Mottling Texture Structure Consistence Boundary Other characteristics
Middle slope soils
Pedon 3 (N 06o40'324'', E 08o51'871'', 105 m ASL
Ap
Bt1
Bt2
Cr1
Cr2
0 – 15
15 – 43
43 – 97
97-137
137-200
10YR 3/2
5YR 4/6
5YR 4/6
10YR 4/6
2.5YR 3/6
-
-
-
10YR 6/6
10YR 6/4
sl
scl
sc
scl
scl
wm gbk
2m sbk
2mc sbk
1mc sbk
mcgbk
ws; mvfr
wss; mvfr
wss; mvfr
wss; mvfr
wss; mvfr
cs
gs
gs
cw
Many common pores;
many few roots; many
quartz; many ants.
Few thin clay cutans on
ped faces; quartz; very
few ants.
Common thin clay
cutans on ped faces;
common medium coarse
roots; quartz; very few
ants.
Common moderate iron
clay cutans on ped faces;
common very few pores;
few fine roots.
Moderate clay cutans on
ped faces; few very fine
pores; quartz.
Pedon 4 (N 06o40'850'', E 08o53'768'', 135 m ASL
Ap
Bt
BC
Cr
0 – 16
16 – 69
69 – 122
122 – 200
10YR 3/3
7.5YR 3/3
5YR 4/6
2.5YR 4/6
-
-
-
-
gsl
gsc
gsc
scl
wmgbk
wm gbk
wm sbk
2m sbk
wns; mfr
ws; mfr
wss; mfr
wss; ,mfi
cs
gw
dw
-
Many common pores;
many coarse roots;
quartz;few ants.
common few roots; ants
Many medium pores;
common medium roots;
iron nodules; quartz;
very few ants;out crop of
sandstone rock.
Common moderate
pores;clay cutans; few
common pores; few fine
roots; iron nodules;
quartz; very few ants.
Common thick clay
cutans on ped faces; few
medium pores; quartz.
Table 2c: Morphological properties of soils at the valley bottom Horizon Depth (cm) Soil Colour
(moist)
Mottling Texture Structure Consistence Boundary Other characteristics
Valley bottom soils
Pedon 5 (N 06o40'197'', E 08o51'873'', 88 m ASL
Ap
Cg1
Cg2
0 – 20
20 - 86
86 – 130
2.5 YR 3/1
2.5 YR 5/6
2.5 YR 5/1
7.5YR 4/4
2.5YR 4/1
5YR 4/6
Scl
scl
c
2mg
2msbk
2msbk
wss; mvfr
ws; mf
wss,mf
cs
gs
-
Few fine roots; worms and
ants.
Very few thin clay cutans on
ped faces; very few pores.
Few thin clay cutans on ped
faces; fine very few pores.
Pedon 6 (N 06o40'758'', E 08o53'737'', 113 m ASL
Ap
Cg
0 – 12
12 – 50
7.5YR 5/1
7.5YR 5/2
-
2.5YR 4/1
Sl
Scl
wfg
wfg
wss; mvfr
wss; mfr
cs
-
Common medium pores;
many medium roots; ants
and cricket.
Common very few pores;
many medium roots; ants.
medium pores; common
medium roots;ants. Foot note: Texture: gr = gravel, Co = cobbles, L = loam, S = sand, C = clay; Structure: 1,2,3 = weak, moderate and strong, f,m.c = fine, medium and
coarse; gr. abk and sbk = granular, angular blocky structure and sub-angular blocky structure; Consistence: w = wet, m = moist, s = slightly sticky, fr =
friable, fi = firm, v = very; Boundary: cs = clear smooth, ds = diffuse smooth, gs = gradual smooth, cw = clear wavy, dw = diffuse wavy, gw = gradual wavy; Asl: Above sea level
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The abundance and size of soil pores seemed to decrease with soil depth and down the slope, especially in the poorly
drained valley bottom. The porous nature of soils in the crest and middle slope may have been responsible for its well-
drained nature giving rise to bright colours.
Soil physical properties
Physical properties of the soils are presented in Tables 3a,b,c. Particle size distribution of the soils indicates that sand
content exceeded 500 g/kg in the surface soils with comparatively lower values in the subsurface soils. Also, values at the
valley bottom appeared lower and suggest limited lateral movement of sand grains. Souza et al. (2019) obtained > 741 g/kg
of sand in the soils overlying Piaui sandstone derived soils in Brazil
High values of sand in the crest and middle slope affirms that the soils were developed in situ while the gently
undulating landscape limited the movement of sand grains downslope. Such values of sand are likely to increase the
infiltration rate, percolation and leaching, and reduce the availability of nutrients in the soil exchange complex. Similar
results were obtained by Lawal et al. (2012) in Muma while higher values were obtained by Ahukaemere et al. (2013) and
Udoh (2015) in the Southeastern and Niger Delta regions of Nigeria. However, Naganori et al. (1984) obtained lower values
in Japan.
Silt fraction was less than 290 g/kg in the entire soils and appeared higher in the valley bottom than other landscape
positions. This suggests the ease with which finer particles are moved compared to sand. The finding agrees with the work
of Naganori et al. (1984), Lawal et al. (2012) and Ahukaemere et al. (2013) while Udoh (2015) obtained values lower than
seen in the present study.
Clay fraction increased vertically downwards and downslope resulting in higher values in the B horizons and the valley
bottom, respectively (Tables 3a,b,c). A further indication that clay particle sizes were easily moved compared to sand sizes.
Table 3a: Physical properties of the soils in the crest
Horizon Depth Sand Silt Clay Text. Bd Pd TP WC Air filled
cm g/kg Mg/m3 %
Pedon 1
Ap 0-33 740 140 120 Sl 1.56 2.5 37.6 4.7 32.86
Bt 33-72 590 100 310 Scl 1.52 2.2 30.9 6.1 24.8
Cr1 72-133 620 190 190 Sl 1.43 2.3 37.8 7.1 30.7
Cr2 133-195 790 90 120 Sl 1.54 2.6 40.7 8.2 32.5
Pedon 2
Ap 0-28 580 180 240 Scl 1.37 2.4 42.9 5.3 37.6
Bt 28-105 490 100 410 Sc 1.26 2.1 40 6.8 33.2
Cr1 105-147 460 160 380 Sc 1.48 2.3 32.7 8.7 24
Cr2 147-200 490 130 380 Sc 1.63 2.2 23.6 9.7 13.9
Surface Mean 660 160 180 Sl 1.47 2.5 40.3 5 35.2
Surface Range 580-740 140-180 120-240 1.37-1.56 2.4-2.50 37.6-42.9 4.74-5.29 32.86-37.6
Subsurface Mean 570 128 300 Scl 1.5 2.3 28 8 26.52
Subsurface Range 460-790 90-190 120-410 1.26-1.63 2.1-2.6 23.6-40.7 6.10-9.72 13.9-33.2
Table 3b: Physical properties of the soils in the middle slope
Horizon Depth Sand Silt Clay Text. Bd Pd TP WC Air filled
cm g/kg Mg/m3 %
Pedon3:
Ap 0-15 720 220 60 Sl 1.4 2.2 36.4 5.26 31.1
Bt1 15-43 610 130 260 Scl 1.5 2.6 42.3 5.84 36.5
Bt2 43-97 580 40 380 Sc 1.65 2.6 36.5 6.97 29.5
Cr1 97-137 540 130 330 Scl 1.48 2.3 35.7 7.94 27.8
Cr2 137-200 540 150 310 Scl 1.28 2.2 41.8 7.02 34.9
pedon 4:
Ap 0-16 680 200 120 Sl 1.42 2.1 32.4 4.32 28.1
Bt 16-69 560 80 360 Sc 1.29 2.8 53.9 6.56 47.3
BC 69-122 490 160 350 Sc 1.35 2.3 41.3 6.93 34.4
Cr 122-200 570 170 260 Scl 1.49 2.3 40.4 8.48 31.9
Surface Mean 700 210 90 Sl 1.41 2.15 34.4 4.79 29.6
Surface Range 680-720 200-220 60-120 1.4-1.42 2.1-2.2 32.4-36.4
4.32-
5.26 28.1-31.1
Subsurface Mean 558 123 321 Scl 1.43 2.44 47.7 7.11 34.6
Subsurface Range 490-610 40-170 260-380 1.29-1.65 2.2-2.8 35.7-53.9
5.84-
8.48 27.8-47.3
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Table 3c: Physical properties of the soils in the valley bottom
Horizon Depth Sand Silt Clay Text. Bd Pd TP WC Air filled
cm g/kg Mg/m3 %
Pedon 5
Ap 0-20 520 260 220 Scl 1.39 2.3 39.6 12.6 27
Cg1 20-86 540 180 280 Scl 1.51 2.4 37.1 14.1 23
Cg2 86-130 390 100 510 C 1.45 2.4 39.6 15.1 24.5
Pedon 6
Ap 0-12 620 290 90 Sl 1.09 2.3 52.6 21.5 31.1
Cg 12.0-50 570 210 220 Scl 1.4 2.3 39.3 24.4 14.9
Surface Mean 570 275 155 Sl 1.24 2.3 46.1 17.1 29.1
Surface Range 520-620
260-
290 90-220 1.09-1.39 - 39.6-52.6 12.6-21.5 27-31.1
Subsurface Mean 500 163 337 1.4 2.4 38.7 17.9 20.8
Subsurface Range 390-570
100-
210 220-510 1.24-1.51 2.3-2.4 37.1-46.1 14.1-24.4 14-24.5 Foot note: BD= Bulk density, Pd= particle density, TP= Total porosity, WC= Water content
Similar findings were reported by Souza et al. (2019) for the sandstone soils of Piaui, Brazil. Increasing clay content with
depth, particularly in the B horizons is indicative of lessivation. Values obtained in this study are higher than those of
Ahukaemere et al. (2013) and Udoh (2015) and corroborates those of Lawal et al. (2012).
The coefficient of variation (CV) of silt and clay down the toposequences were 22 and 27 %, respectively for the
surface soils, while sand had very low values. This suggests that surficial erosion or lateral movement encourages mainly
fine particles; clay and silt.
The bulk density values ranged between 1.09 in the valley bottom and 1.65 Mg/m3 in the middle slope of the soils
(Tables 3a,b,c). Irrespective of the landscape positions, the surface mean values were within 1.1 – 1.4 Mg/m3 suggested for
cultivated loams (Donahue et al., 1983), but were less than 1.60 Mg/m3. This indicates that air and water movement in the
soils are optimum for plant growth (Esu, 2010). Also, particle density was slightly less than 2.65 Mg/m3 (Table 2)
recommended for mineral soils in the tropics (Blake, 1965). Such values may indicate lower amounts of oxides of Fe and
Mn in the soils. Bulk and particle densities had very low variability with landscape position (CV < 7 %).
Forms of porosity and values obtained are presented in Tables 3a,b,c. Mean values of total porosity were less than 50
% while air-filled porosity (macro porosity) exceeded 25 % and volumetric water content (micro porosity) was quit low for
the surface and subsurface soils of all the landscape positions. However, very high CV of water content (> 40 %) between
landscape positions irrespective of soil depth, indicates variation in soil drainage with depth and landscape position and
agrees with the concept of a catena. Total porosity values were within the range of values obtained by Ahukaemere et al.
(2013) in the false bedded sandstone derived soils of Southeastern Nigeria; however, Ahukaemere and Akpan (2012) had
higher values of 26.76 – 43.02 % in soils of Amasiri in Ebonyi State, Nigeria.
Chemical properties of the soils
Results of chemical properties of the soils are presented in Table 4. Mean soil pH values were comparatively higher
in the subsurface soils (Table 4), and rated as severely and moderately acid for the entire soils (Holland et al., 1989). Low
pH in sandstone derived soils is attributed to low soil base status (Souza et al., 2019). This indicates that significant amounts
of exchangeable Al3+ and H+ may be present to significantly affect plant growth (Esu, 2010). The pH seems to have been
more influenced by exchangeable H+ as its values were higher than exchangeable Al3+ in over 95 % of the horizons (Table
4). Consequently, exchangeable Al3+ was generally less than 2.1 cmol/kg as recommended by Holland et al. (1989) for most
arable crops. Such values are not likely to be toxic to plant roots as to affect its proliferation. Sandstone derived soils seem
to vary in pH with location (Ahukaemere et al., 2013; Bulktrade, 1989). However, the pH values obtained by Ukut et al.
(2014) in similar soils elsewhere were similar to those obtained in the present study. Very low CV for soil pH indicates that
it is poorly influenced by the toposequences while exchangeable acidity had values that were > 20 %.
Soil organic carbon was rated low in the crest and valley bottom, but moderate in the middle slope (Table 4) (Holland
et al., 1989). The low soil organic carbon may be attributed to organic matter mineralization, loss to leaching, and bush
burning. These values agree with those of Bulktrade (1989) in the Bekwarra area and vary with those of Ogunwale and
Ashaye (1975). The CV of organic C was greater than 20 % and indicates variability with landscape position imposed by
land use. Total N had similar trend as organic C and was rated as low to very low (Table 4) in the entire soils (Holland et
al., 1989). According to Eshett (1985), low nitrogen in an area is attributed to crop removal and rapid mineralization of
organic matter. Laffan et al. (1998) obtained similar results in Northern Tasmania, New Zealand.
The C/N values were less than the separating index of 25 (Paul and Clark, 1989) and 20 (Agbede, 2009) (Table 4),
and were rated low. This ratio will encourage high level of microbial activity, increased decomposition of organic matter
and corresponding release of nutrient elements into the soil solution for plant root uptake (Akpan-Idiok and Ofem, 2014).
Available P was rated low (Holland et al. 1989) in the entire soils, however, the middle slope soils appeared to be
comparatively higher than other landscape positions (Table 4). The surface soils had higher variation (CV) with landscape
positions than the subsurface soils. Surface soils are most often manipulated than subsurface soils. This may be due to the
influence of agricultural activities such as tillage, manure/fertilizer application, and fecal manure/fertilizer application, and
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Table 4: Chemical properties of the soils in the crest
Horizon Depth pH O C T.N C/N Av.P Ca Mg K Na Al3+ H+ EA CEC CEC/Clay BS Ca/Mg Mg/K
cm H2O g/kg mg/kg cmol/kg %
Crest
Pedon 1: Typic Haplustalf (Haplic Acrisols)
Ap 0-33 5.5 0.64 0.05 12.8 11 4 1 0.1 0.07 0.8 0.4 1.2 15 1.25 81 4 10
Bt 33-72 6 0.56 0.04 14 6 7.8 3 0.12 0.09 0.8 0.4 1.2 15 0.48 90 2.6 25
Cr1 72-33 6 0.09 0.01 9 7 8 3.6 0.12 0.08 0.8 0.4 1.2 16 0.84 91 2.22 30
Cr2 133-195 5.9 0.09 0.01 9 3.12 6.5 1.5 0.11 0.09 0 1.2 1.2 15 1.25 87 4.33 13.64
Pedon 2: Typic Paleustalf (Haplic Acrisols)
Ap 0-28 5 0.84 0.07 12 1.75 4.8 0.8 0.13 0.1 0.08 0.08 0.16 25 1.04 78 6 6.15
Bt 28-105 5.5 0.38 0.02 19 1.25 5.8 1.4 0.1 0.09 1.2 1.2 2.4 15 0.37 75 4.14 12.73
Cr1 105-147 5.8 0.38 0.02 19 0.37 6 1.4 0.11 0.08 1.2 0.8 2 26.6 0.68 79 4.29 12.73
Cr2 147-200 6 0.14 0.01 14 0.3 8.8 2.4 0.12 0.08 1.6 0.4 2 25 0.66 85 3.67 20
Surface mean 5.25 0.74 0.06 12.4 6.4 4.4 0.9 0.12 0.07 0.44 0.6 0.68 20 1.15 79.5 5 8.08
surface range 5.0-
5.5
0.64-
0.84
0.05-
0.07
12.0-
12.8
1.75-
11.0
4.0-
4.8
0.8-
1.0
0.10-
0.13
0.07-
0.10
0-
0.80
0.40-
0.80
0.16-
1.2
15.0-
25 1.04-1.25
78.0-
81.0
4.00-
6.00
6.15-
10
Subsurface mean 5.9 0.27 0.02 14 3 7.15 2.22 0.11 0.06 0.69 0.73 1.67 18.67 0.71 84.5 3.21 16.9
subsurface range 5.5-6 0.09-
0.56
0.01-
0.04 9.0-19
0.30-
7.00
5.8-
8.8
1.4-
3.6
0.10-
0.12
0.08-
0.09
0-
0.16
0.40-
0.12
1.20-
2.4
15.0-
26 0.37-0.84
75.0-
91.0
2.22-
4.33
12.73-
30
middle slope
pedon 3: Typic Paleustalf (Haplic Acrisols)
Ap 0-15 5.2 0.84 0.07 12 9.25 7.6 1.8 0.12 0.09 0 0.8 0.8 14 2.33 92 4.22 15
Bt1 15-43 5 0.32 0.02 19 1 5.2 0.8 0.1 0.07 0.24 2.56 2.8 30 1.15 69 6.5 8
Bt2 43-97 5.8 0.32 0.02 19 5.25 5 0.6 0.1 0.07 2.4 0.4 2.8 26 0.68 66 8.39 6
Cr1 97-137 5.8 0.08 0.01 8 1.25 5.6 0.8 0.11 0.09 1.6 1.2 2.8 18 0.55 70 7 7.27
Cr2 137-200 5.8 0.16 0.01 16 1.25 4.2 1.4 0.1 0.08 1.2 1.6 2.8 27 0.87 67 3 14
pedon 4: Typic Paleustalf (Rhodic Luvisols
Ap 0-16 5.3 1.54 0.13 11.8 6.12 6 1 0.11 0.08 0.8 0.4 1.2 14 1.17 86 6 9.09
Bt 16-69 5 0.8 0.07 11.4 2.5 5 0.8 0.12 0.09 1.2 1.6 2.8 26 0.72 68 6.25 6.67
BC 69-122 5.1 0.16 0.01 16 1.12 5.6 1 0.11 0.08 0.8 1.2 2 17 0.49 77 5.6 9.09
Cr 122-200 5.2 0.1 0.1 10 0.5 5.8 1.2 0.12 0.1 0.8 0.4 1.2 18 0.69 87 4.83 10
Surface mean 5.25 1.19 0.1 11.9 7.67 6.8 1.4 0.12 0.09 0.4 0.6 1 14 1.75 89 5.11 14.5
surface range 5.20-
5.30
0.84-
1.54
0.07-
0.13
11.8-
12.0
6.12-
9.25
6.0-
7.6
1.0-
1.8
0.11-
0.12
0.08-
0.09
0.00-
0.08
0.40-
0.80
0.8-
1.2
0.0-
14.0 1.17-2.33
86.00-
92,00
4.22-
6.00
9.09-
15.00
Subsurface mean 5.39 0.17 0.02 14.2 1.84 5.2 0.94 0.11 0.08 1.18 1.28 2.46 23.1 0.74 72 5.93 8.02
subsurface range 5.0-
5.8
0.08-
0.32
0.01-
0.07
8.0-
19.0
0.50-
5.25
5.0-
5.8
0.6-
1.4
0.10-
0.12
0.07-
0.10
0.24-
1.60
0.40-
2.56
1.20-
2.8
17.0-
30.0 0.49-0.87
66.00-
87.00
3.00-
8.39
6.00-
10.00
Footnote: OC (Organic carbon); T.N (Total nitrogen); Av.P (available phosphorus); EA (Exchangeable acidity); CEC (cation exchange capacity); BS (Base saturation)
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fecal and leaf dropping as well as surficial erosion.
The soils exchange complex was dominated by exchangeable Ca2+ and Mg2+ with values that were rated as moderate (Holland et al., 1989). Souza et al. (2019) also reported the
dominance of Ca and Mg ions in sandstone derived soils in Piaui, Brazil. Exchangeable Ca had a range of 4 – 8.8 cmol/kg while exchangeable Mg ranged from 0.8 to 3.6 cmol/kg in the
entire soils (Table 4). Values of exchangeable K+ and Na+ were rated low as they were less than 0.13 and 0.10 cmol/kg (Table 4), respectively (Holland et al., 1989). Souza et al. (2019)
reported very low values for exchangeable K in
Table 4 Contd.
Horizon Depth pH O C T.N C/N Av.P Ca Mg K Na Al3+ H+ EA CEC CEC/Clay BS Ca/Mg Mg/K
cm g/kg mg/kg cmol/kg %
valley bottom
pedon 5: Aquic Udorthents (Hypereutric Gleysols)
Ap 0-20 5.2 0.86 0.07 12.28 1.12 5.4 0.8 0.1 0.08 0.8 0.4 1.2 32 1.45 84 6.75 8
Cg1 20-86 5.7 0.36 0.02 18 5.5 6.8 1.4 0.11 0.07 0 1.2 1.2 26 0.93 87 4.86 12.73
Cg2 86-130 5 0.16 0.01 16 3.12 5.4 1.6 0.1 0.07 0 0.4 0.4 50 0.98 94 3.38 16
pedon 6: Aquic Udorthents (Hypereutric Gleysols)
Ap 0-12 5.4 0.94 0.08 11.75 2.37 5.6 1 0.11 0.08 0.8 0.4 1.2 15 1.67 85 5.6 9.09
Cg 12-50 5 0.72 0.06 12 0.87 5 1 0.1 0.08 2 2.8 4.8 14 0.64 62 5 10
Surface mean 5.3 0.9 0.075 12.05 1.75 5.5 0.9 0.11 0.08 0.8 0.4 1.2 23.5 1.56 84.5 6.18 8.55
surface range 5.20-
5.40
0.86-
0.94
0.07-
0.08
11.8-
12.3
1.12-
2.37
5.4-
5.6
0.80-
1.00
0.10-
0.11
0.00-
0.08
0.00-
0.80
0.00-
0.40
0-
1.20
15.0-
32 1.45-1.67
84.0-
85.0
5.60-
6.75
8.00-
9.09
Subsurface mean 5.23 0.41 0.03 15.33 3.16 5.73 1.33 0.1 0.07 0.67 1.47 2.13 30 0.85 81 4.41 12.9
subsurface range 5.00-
5.70
0.16-
0.72
0.01-
0.06
12.0-
18.0
0.87-
5.50
5.0-
6.8
1.00-
1.60
0.10-
0.11
0.07-
0.08
0.00-
2.00
0.40-
2.80
0.40-
4.8
14.0-
50 0.64-0.98
62.0-
94.0
3.38-
5.00
10.0-
12.73
Footnote: OC (Organic carbon); T.N (Total nitrogen); Av.P (available phosphorus); EA (Exchangeable acidity); CEC (cation exchange capacity); BS (Base saturation)
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sandstone derived soils with values approaching zero. These results are similar to those of Bulktrade (1989) in the study
area. The exchangeable bases may have been weakly held in the exchange complex and then leached from the porous and
sand dominated soils of the area. Soils limiting in K+ with coarse textures may not be highly suitable for Oil palm cultivation
(Ofem et al., 2016), hence the evaluation of same soils for cashew production.
The exchangeable bases had CV values in the order Mg > Ca > Na > K, with Mg being the most variable down the
toposequences.
Cation exchange capacity by NH4OAc at pH 7.0 in the soils had ranges of 14-23.5 and 18.67-30.0 cmol/kg in the
surface and subsurface soils (Table 4), respectively. These values are moderate to high (Holland et al., 1989). Lower values
(<8.8 cmolc/kg) of CEC were reported by Souza et al. (2019). They further attributed the values to low clay content. Higher
subsurface values indicate that clay may have been more responsible for the soils exchange capacity than organic matter.
The soils are likely to encourage plants nutrients uptake and increase crop yield. Bulktrade (1989) obtained similar results
in the study area while Udoh (2015) obtained lower values for similar soils elsewhere. The CV of CEC7 in the surface soils
was > 20 % and indicates higher variability in the surface soils of the toposequences.
Base saturation (BS) values ranged between 66 and 92 % in the middle slope and crest and 14 - 50 % in the valley
bottom (Table 4). Such values are high to very high (Holland et al., 1989) and indicate that the basic cations are in readily
available forms for plant root uptake and correlates with the low values obtained for exchangeable aluminum which was
within permissible levels. Similar values were obtained by Bulktrade (1989) and Udoh (2015) for sandstone soils in
Bekwarra and Niger Delta region of Nigeria, while Naganori et al. (1984) obtained very low to moderate base saturation for
the shattered sandstone soils in Southeast, Nigeria. The CV of BS down the toposequences was less than 7 % and described
as low.
The Ca-Mg ratio in the soils was either within the range of 3:1 to 5:1 or slightly higher than recommended for
productive soils (Landon, 1991), an indication that the interaction between Ca and Mg is appropriate for the growth of crops.
Though with moderate levels of Mg and low K, the ratios of the cations were high when compared to the critical level of
1:2 for productive soils (Landon, 1991). This indicates that the interaction between Mg and K in the soils is high enough to
support the growth of crops. Mg in the form of Mg2+ is more likely to be available to crop plants in the soil relative to K
(Akpan-Idiok and Ofem, 2014).
Soil classification Pedons in the crest and middle slope had high base saturation (NH4OAc pH 7) below the upper boundary of the argillic
B horizons with values greater than 50 % as well as Ochric epipedons. The soils qualified as Alfisols. Ustic soil moisture
regime qualified them as Ustalfs. Values obtained for CEC/clay in pedon 1 were also greater than 16 cmol/kg in all sub
horizons with percent decrease in clay of > 20 % from horizons with maximum clay content. The soil qualified as Haplustalf.
However, pedons 2 (crest), 3 and 4 (middle slope) had no densic, lithic or paralithic contacts within 150 cm of the soil
surface. Also, with increasing depth the soils do not have clay decrease of 20 % or more from the maximum clay content
while chroma of 5 or more was obtained with Hue of 7.5YR and 10YR in the argillic horizon of pedon 4 and Cr1 horizon
of pedon 3 respectively. Pedons 2, 3 (Haplic Acrisols) and 4 (Rhodic Luvisols) qualified as Paleustalfs in the greatgroup
and as Typic Paleustalf at the subgroup category while pedon 1 (crest) qualified as Typic Haplustalf (Haplic Acrisols).
Valley bottom soils were formed over alluvium, shallow to water table and without pedogenic horizons except Ochric
epipedons. They qualified as Entisols; however, the soils fail to meet the criteria of other suborders in Entisols and are
classified as Orthents and as Udorthents in the great group category. Consequently, the soils have in all horizons but one
within 100 cm of the mineral soil surface, chroma of 2 or less and also aquic conditions for some time of normal years. The
soils in the valley bottom qualified as Aquic Udorthents (Hypereutric Gleysols) at the suborder category.
Land evaluation for cashew production
Climate, wetness, physical soil properties as well as fertility qualities were optimum or near optimum for cashew
production except limitations occasioned by organic C and available nutrients (a). However, poorly drained soils of pedons
5 & 6 were in addition, limited by poor drainage. Current index of productivity of the soils indicate that 33.3 % of the soils
were marginally suitable (pedons 2 & 4), another 33.3 % was currently not suitable (pedons 1 & 3) while 33.3 % was
permanently not suitable (pedons 5 & 6) for the production of cashew. The soils were mainly limited by organic carbon and
available nutrients (total N, available P and exchangeable K) while the poorly drained soils (pedons 5 & 6) were in addition,
limited by poor drainage and flooding. Organic matter content correlates with cashew nut/m2 (Ngatunga et al., 2001) and
acts as the main source of phosphorus (Bleeker & Laut, 1987). Available P is an essential component of the cell nucleus in
cashew (Widatmaka et al., 2014), however, delay maturity as well as shriveled seeds are sensitive symptoms of its deficiency
(Aikpokpodion et al., 2009; Widiatmaka et al., 2014a). Consequently, Ibiremo et al., (2012) advocated the use of rock
phosphates for treatment, while amended organic fertilizer improves the growth of the crop (Adeigbe et al., 2015).
Potential index of productivity (IPp) presents a situation where measures are put in place to remove limitations present
in IPc. Figs. 2a and b show the suitability classes for Cashew production in Anyikang and Ibiaragidi. Out of a total area of
82.17 ha evaluated, 65.3 % was moderately suitable while 34.7 % of the land area was not suitable for Cashew production
in Anyikang. Similarly, Ibiaragidi occupied a total area of 38.08 ha with 77.5 % considered moderately suitable while 22.5
% was not suitable for cashew production.
Limitations due to organic C, total N and available P were removed by simple application of organic matter (composted
animal droppings and plant residues). Consequently, 66.7 % of the soils (pedons 1, 2, 3 & 4) were upgraded to moderately
suitable status while 33.3 % were currently not suitable (pedons 5 & 6).
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On the contrary, Udoh et al. (2015) classified the sandstone soils of Akwa Ibom as highly and moderately suitable for
cashew production. It is therefore necessary to make a change of the current land use for the tract of land. Major limitations
were due to availability of nutrients (a) expressed by exchangeable K in the entire soils while drainage caused a major
challenge for soils in the poorly drained areas. Results obtained by Udoh (2015) identified soil physical properties as the
main constraint for cashew production in Akwa Ibom state. Poorly drained soils have reduced availability for exchangeable
cations (Bleeker & Laut, 1987) while nitrogen has been described as a necessity during the growth stage of cashew tree
(O’Farrell et al., 2002). It is important therefore, to increase N, P and exchangeable K for increased production of cashew
(Widiatmaka et al. 2014).
Fig. 2a: Potential suitability classes for Anyikang
Fig. 2b: Potential suitability classes for Ibiaragidi
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Table 5: Land characteristics data and rating of the soils
N/B: MAR; Mean annual rainfall, MAT; Mean annual temperature, FGW; fluctuating ground water, IPc; Current or actual index of productivity, IPp; potential index of productivity;
w; wetness, f; soil fertility, a; available nutrients, S2; Moderately suitable, S3; Marginally suitable, N1; Temporarily not suitable, N2; Permanently not suitable for the land use under
consideration
Ped MAR MAT Flood Drain. Text Depth CEC BS pH OC TN AP Exch. K IPc IPp
mm/yr oC cm cmol/kg % (H2O) g/kg (ppm) (cmol/kg)
1 1983 27.9 Fo Good SL 195 15.3 87 5.9 0.35 0.03 6.8 0.11
S1(100) S1(100) S1(100) S1(100) S1(90) S1(100) S1(100) S1(100) S1(100) S3(55) S3(55) S2(70) S2(70) N1fa(38.7) S2a(66.4)
2 1983 27.9 Fo Good SC 150 22.9 85 5.6 0.44 0.03 0.92 0.12
S1(100) S1(100) S1(100) S1(100) S1(95) S1(100) S1(100) S1(100) S1(97) S3(60) S3(55) S3(58) S2(72) S3fa(41.5) S2a(69.1)
3 1983 27.9 Fo Good SCL 145 23 73 5.5 0.34 0.03 3.6 0.11
S1(100) S1(100) S1(100) S1(100) S1(90) S1(100) S1(100) S1(100) S1(95) S3(55) S3(55) S2(65 S2(70) N1fa(38.7) S2a(59.9)
4 1983 27.9 Fo Good SCL 87 18.8 80 5.2 0.65 0.08 2.56 0.12
S1(100) S1(100) S1(100) S1(100) S1(90) S1(100) S1(100) S1(100) S1(85) S3(60) S3(60) S2(64) S2(72) S3fa(44.1) S2a(63.0)
5 1983 27.9 F1 FGW SCL 200 36.0 88 5.3 0.46 0.03 3.25 0.10
S1(100) S1(100) S3(45) S2(65) S1(90) S1(90) S1(100) S1(100) S1(88) S3(50) S3(55) S2(65) S2(60) N2wfa(22.4) N1wa(31.0)
6 1983 27.9 F1 FGW SL 180 14.5 74 5.2 0.83 0.07 1.62 0.11
S1(100) S1(100) S3(45) S2(65) S1(90) S2(60) S1(100) S1(100) S1(85) S3(60) S3(60) S2(60) S2(70) N2wfa(20.9) N1wa(26.9)
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Conclusion and recommendations The morphological, physical and chemical properties as well as classification of sandstone derived soils of Southern
Guinea savanna in Bekwarra LGA were studied at various landscape positions and variability obtained in most soil
properties. The soils were low in exchangeable cations and low to moderate in organic carbon with sand dominating the soil
particle size distribution. However, soil CEC was moderate to high. At the subgroup category, pedon 1 was classified as
Typic Haplustalf (Haplic Luvisols) while pedons 2 and 3 were classified as Typic Paleustalf (Haplic Luvisols) and pedon 4
as Typic Paleustalf (Rhodic Luvisols). Pedons 5 and 6 qualified as Aquic Udorthents (Hypereutric Gleysols). Land
suitability evaluation indicated that the soils are most likely to improve upon proper management. Current index of
productivity indicated marginal (S3) and not suitable classes (N1 & N2) which further advanced to moderately suitable (S2)
and currently not suitable (N1), potentially for cashew production. It is advocated that farmer education should be intensified
with the following site specific soil management procedures:
1. A combination of organic and inorganic fertilizers (Potassic fertilizer) should be used to boost soil productivity in the
area.
2. Extremely acid soils affect the activities of most soil microbes and the availability of nutrients. Application of calcite and
dolomite would not only attempt to solve acidity problems but also increase nutrients such as calcium and magnesium in
the soils.
3. Mulching with organic plant residues should be encouraged. This will reduce the speed of run off and increase soil organic
matter content thereby improving the structure of the sand dominated soils.
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AUTHORS
First Author – Ofem, K. I, Department of Soil Science, University of Calabar, Nigeria
Second Author – Abua, S. O, Department of Soil Science, University of Calabar, Nigeria
Third Author – Umeugokwe, C. P, Department of Soil Science, University of Nigeria, Nsukka
Fourth Author – Ezeaku, V. I, Department of Soil Science, University of Nigeria, Nsukka
Fifth Author – Akpan-Idiok, A. U, Department of Soil Science, University of Calabar, Nigeria